This invention relates to a process for separating 1-nitro-anthraquinone from an anthraquinone nitration mixture in concentrated nitric acid.
Anthraquinone can be nitrated in sulphuric acid, phosphoric acid, hydrofluoric acid and nitric acid to form 1-nitro-anthraquinone. In all these media, and especially in nitric acid, 2-nitro-anthraquinones and dinitro-anthraquinones are produced in addetion to the desired 1-nitro-anthraquinone (see N. S. Dokunichin and Z. Z. Moiseeva, Z. vses. chim. Obsc. 11, 35 (1966); Houben-Weyl, Methoden der organischen Chemie Volume 10/1, 614 (1971)). Various methods have been proposed for separating or purifying 1-nitro-anthraquinone, e.g. the treatment of crude 1-nitro-anthraquinone with acid amides according to German Auslegeschrift No. 2 039 822; treatment with halogenated alkanes according to German Offenlegungsschrift No. 2 142 100; treatment with aqueous solutions of sodium sulphite according to U.S. Pat. No. 2 302 729; or the recrystallisation from suitable solvents, for example from glacial acetic acid, and finally distillation according to German Patent Specification No. 281 490. In all these methods, the removal of anthraquinone and 1,5-dinitro-anthraquinone at the same time gives rise to difficulties.